As a novel gyroscope, optical fiber gyroscope uses optical fiber as carrier for laser beam and utilizes Sagnac effect in a closed optical fiber loop to measure the rotational angular velocity of a rotating body. Since its emergence, optical fiber gyroscope has received general attention from universities and scientific research institutions in many countries in the world, thanks to its outstanding advantages, structural flexibility, and attractive prospect, and has achieved great progress in the last twenty years. As the demand for optical fiber gyroscope continuously increases, the requirements for miniaturization, integration, low cost, and high stability are put forth for optical fiber gyroscope.
At present, the integrated optical chips that are widely used in optical fiber gyroscope systems are integrated chips that are based on LiNbO3 material. Since these integrated chips usually have Y branches of proton-exchanged LiNbO3 optical waveguide, they are also called as Y-type waveguide integrated optical devices (multi-functional integrated optical chips (MFIOC) in foreign countries). Such a device integrates Y-type beam splitter, polarizer, and phase modulator in a same chip, and can be applied in closed-loop optical fiber gyroscopes with various accuracies. Though such integrated optical chips are the best in terms of practical application in integrated optical fiber gyroscopes, but they have the following drawbacks during application:    1. When the optical signal returns from the optical fiber coil and enters into a Y-shape waveguide, a part of the signal will leak and dissipate in the substrate, generates a leak pattern, and thereby affects the accuracy of optical fiber gyroscope.    2. The production method of LiNbO3 optical waveguides is proton exchange method, which has strict requirements for proton exchange time, temperature, properties of the exchange medium, and annealing temperature and time. The process is complex and the cost is high;    3. Phase modulation must be performed for LiNbO3 optical waveguides. To that end, modulation electrodes must be prepared at two ends of optical waveguide by utilizing electro-optic effect. Therefore, the preparation process becomes more complex, and the modulation efficiency is not high.
In recent years, with the development of nano-science and nano-electronics, a brand-new waveguide structure, SPPs (Surface Plasmon Polaritons) waveguide, became a new research direction in the integrated optic field. SPP is a kind of non-radioactive electromagnetic wave that propagates on metal surface and is restrained thereon. SPP is restrained on the waveguide surface due to the interaction between light and free electrons of metal. SPP waveguide has unique features that are not available in ordinary optical waveguides, for example: the signals can be transmitted at nanometer scale; the signals are maintained in single polarization state in the long-distance transmission process, and therefore mono-mode transmissions can be implemented at various sizes; the metal core layer structure of SPP waveguide can transmit not only optical signals but also electrical signals, and therefore hybrid optical/electrical transmission can be implemented on the same chip; the dielectric constants of metal is complex number, wherein, the imaginary part represents the optical absorbing capability of the metal, therefore quick signal attenuation can be achieved with appropriate design of the metal core layer; the metal core layer of SPP waveguide can be directly modulated, so as to achieve efficient tuning of the SPP waveguide device. Thanks to these unique features of SPP waveguide, SPP waveguide devices play an important role in the optical communication and optical sensing field.